1. Field of the Invention
The present invention relates to an arrangement and method for detecting an interference in a receive signal in a TDMA (Time Division Multiple Access) communications system.
2. Description of the Prior Art
TDMA techniques, in addition to the current extensive use thereof in satellite communication arrangements, have recently assumed an important role in mobile communications systems.
While the present invention will be discussed in connection with a TDMA mobile communication system, it will be understood that it may also be applied to a TDMA satellite communications system without departing from the concept underlying the instant invention.
In a TDMA mobile communications system, plural mobile units located within a given service area are respectively allowed to communicate with a land site using allocated time slots of each consecutive TDMA frame. The time slot used by a given mobile unit has therefore the same period as the TDMA frame.
In the event that a land site detects a predetermined number of interferences in a receive signal(s) within a given time duration, it is necessary to change the data carrier frequency currently in use to another one to avoid communication degradation.
Before turning to the present invention it is deemed preferable to discuss a known arrangement for detecting the presence of interferences in a receive signal(s) in a TDMA mobile communications system.
FIG. 1 is a block diagram schematically showing a land site 6 which includes a known interference detecting arrangement. The portions of the land site 6, which are deemed irrelevant to the instant invention, are not shown for the sake of brevity.
In FIG. 1, a plurality of mobile units Ma-Mn are located within a service area which is covered by the land site 6. A receiver 10 which forms part of the land site 6 is supplied, via an antenna 12 and a duplexer 14, with a burst signal(s) transmitted from one or more of the mobile units Ma-Mn. The receiver 10 demodulates the incoming burst signal and subsequently outputs a corresponding base band signal S8. A transceiver control section 8 includes a transceiver controller 16, a sampling circuit 18 and a microcomputer 20. The base band signal S8 is applied to the transceiver controller 16 via a line L8. A transmitter 22 is interconnected between the transceiver controller 16 and the duplexer 14 as shown.
The sampling circuit 18 receives a signal S10 from the receiver 10. The signal S10 is generated at an IF (Intermediate Frequency) stage (not shown) of the receiver 10 and indicates electric field strength of each of the signals in the time slots of the TDMA frame. The sampling circuit 18 samples the signal S10 in synchronism with a clock CLK applied thereto from the transceiver controller 16. The clock CLK comprises a train of pulses each of which is generated in synchronism with time slots of a TDMA frame. The sampling circuit 18 applies, via a line L14, the output thereof (viz., sampled data) S12 to the microcomputer 20. The microcomputer 20 includes a ROM (not shown) for storing a program dedicated to detecting the interference in the receive signals.
In more specific terms, the land site controller (not shown) informs, via a line L16, the transceiver controller 16 of the overall use of the time slots of a TDMA frame. This information which indicates the current use of the time slots is also applied to the transmitter 22 as a signal S14 over the line L11. The transmitter 22 receives a base band signal from the transceiver controller 16 via the line L10 and implements time slot data transmission using the signal S14.
The microcomputer 20 receives the output signal S12 via the line L14 and also receives the information indicating the current use of the time slots via a line L12. This information applied to the microcomputer 20 via the line L12 corresponds to the signal S14. Following this, the microcomputer 20 checks to see, using the program stored in the ROM therewithin, whether or not the output signal S12 is detected within the time slot not in use. If this happens, interference in the data communication channel currently used is indicated. The microcomputer 20 advises the transceiver controller 16 of the presence of interference. Further, the land site controller is advised of the detection of interference from the transceiver controller 16, and changes the communication channel to another one if necessary. The manner in which the current carrier frequency is changed to a new one is not directly concerned with the present invention, and hence will not be discussed in detail for the sake of brevity.
With the recent trend in high speed data transmission in a TDMA communications system, the above-mentioned prior art has encountered the problem in that the detection of the interference is extremely difficult or nearly impossible through the use of software. The reason for this is that the speed with which the interference detection routines can be executed are limited and are often unable to follow the high speed incoming data.